Papers by Christopher Walton
IEEE/LEOS International Conference on Optical MEMS and Their Applications Conference, 2006., 2006
OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), 2003
Complex target structures are necessary to take full advantage of the unique laboratory environme... more Complex target structures are necessary to take full advantage of the unique laboratory environment created by inertial confinement fusion experiments. For example, uses-ofignition targets that contain a thin layer of a low density nanoporous material inside a spherical ablator shell allow placing dopants in direct contact with the DT fuel. The ideal foam for this application is a low-density hydrocarbon foam that is strong enough to survive wetting with cryogenic hydrogen, and low enough in density (density less than ~30 mg/cc) to not reduce the yield of the target. Here, we discuss the fabrication foamlined uses-of-ignition targets, and the development of low-density foams that can be used for this application.
Journal of Magnetism and Magnetic Materials, 1999
The status of polarizing optical elements for the vacuum ultraviolet and soft X-ray range extendi... more The status of polarizing optical elements for the vacuum ultraviolet and soft X-ray range extending from roughly 50 to 2000 eV are reviewed, as are some of their emerging applications in magneto-optical studies utilizing synchrotron radiation. The optics include tunable linear polarizers and birefringent phase retarders based on multilayer interference structures, and circular polarizing filters based on magnetic circular dichroism. Magneto-optical capabilities enabled by these optical elements include measurement of Faraday and Kerr rotation spectra and hysteresis loops, and the conversion of linear to circular polarization and helicity switching. Circular polarizers combined with scanning zone plate microscopes yield magnetization contrast in transmission imaging. Examples using these capabilities to study polycrystalline Fe films and Fe/Cr multilayers are given. Resonant soft X-ray magneto-optical spectroscopies are especially relevant to obtaining an understanding of magnetism on a microscopic level in complex materials and nanostructures because their element-specific signals can be larger than in other spectral ranges. Combined with scattering and microscopy techniques these spectroscopies can provide depth sensitive and lateral spatial resolution on the nanometer scale.
Given the existing X-ray laser sources near 45 nm it would be useful to produce efficient X-ray o... more Given the existing X-ray laser sources near 45 nm it would be useful to produce efficient X-ray optics in the 35 to 50 nm wavelength range that could be utilized in new applications. In this work we are developing the process to stabilize the interfaces of nanolaminate structures using materials such as Sc and Si. These materials will enable us to develop new multi-layer mirror technology that can be used in the wavelength range near 45 nm. To obtain this objective, the interfacial structure and reaction kinetics must first be well understood and then controlled for design applications. In this work we fabricate several Sc/Si multi-layer mirrors with and without a B 4 C barrier layer. The structure and reflectivity of the mirrors are analyzed.
Applied Optics, 2007
This manuscript discusses the multilayer coating results for the primary and secondary mirrors of... more This manuscript discusses the multilayer coating results for the primary and secondary mirrors of the Micro Exposure Tool (MET): a 0.30-numerical aperture (NA) lithographic imaging system with 200×600 µm 2 field of view at the wafer plane, operating in the extreme ultraviolet (EUV) wavelength region. Mo/Si multilayers were deposited by DCmagnetron sputtering on large-area, curved MET camera substrates, and a velocity modulation technique was implemented to consistently achieve multilayer thickness * R. M. Hudyma was with LLNL when this work was performed. 1 profiles with added figure errors below 0.1 nm rms to achieve sub-diffraction-limited performance. This work represents the first experimental demonstration of sub-diffractionlimited multilayer coatings for high-NA EUV imaging systems.
A series of hafnia/silica, oblique incidence (56°), 1064 nm high reflectors (HRs) were prepared ... more A series of hafnia/silica, oblique incidence (56°), 1064 nm high reflectors (HRs) were prepared and coated with silica overlayers of varying optical thickness from λ/2 to 4λ in order to determine the effect of an overlayer on the laser-damage resistance of the HRs. The stress and laser damage thresholds for S and P polarization of the HRs were measured, and
Spie Proceedings Series, 2001
A micro beam Faraday cup assembly includes a refractory metal layer with an odd number of thin, r... more A micro beam Faraday cup assembly includes a refractory metal layer with an odd number of thin, radially positioned traces in this refractory metal layer. Some of the radially positioned traces are located at the edge of the micro modified Faraday cup body and some of the radially positioned traces are located in the central portion of the micro modified
Thesis University of California Berkeley Source Dai B 59 03 P 1317 Sep 1998 139 Pages, Nov 30, 1997
To satisfy mesh spacing constraint delta/lambdaDebye<=1 particle In Cell (PIC) simulations at ... more To satisfy mesh spacing constraint delta/lambdaDebye<=1 particle In Cell (PIC) simulations at 25x reduced cathode currents levels are used to numerically model the distribution of currents, electrostatic potentials and particle kinetics in a Type II ``unbalanced'' cylindrically symmetric magnetron discharge used for Be sputter coating of ICF capsules. Simulation indicates a strong magnetic field confinement of the plasma in the closed field lines region adjacent to cathode, and accompanying cross-field line plasma diffusion into the open-field line region connected to wall/anode. A narrow Charles-Langmuir sheath and a pre-sheath that is ˜10x wider due to the existence of the B-field are observed. The effects of varying boundary conditions, e.g., the separation between the anode/cathode, the anode bias voltage, etc., are studied, which is expected to aid experimentalists in turning these ``knobs'' for better coating qualities. We also show that the etch rate due to sputtering of Be targets predicted by the results of our PIC simulations, after rescaling to experimental conditions, agrees with experiments.
ACS applied materials & interfaces, Jan 30, 2015
Hollow spheres with uniform coatings on the inner surface have applications in optical devices, t... more Hollow spheres with uniform coatings on the inner surface have applications in optical devices, time- or site controlled drug release, heat storage devices, and target fabrication for inertial confinement fusion experiments. The fabrication of uniform coatings, which is often critical for the application performance, requires precise understanding and control over the coating process and its parameters. Here, we report on in-situ real-time radiography experiments that provide critical spatio-temporal information about the distribution of fluids inside hollow spheres during uniaxial rotation. Image analysis and computer fluid dynamics simulations were used to explore the effect of liquid viscosity and rotational velocity on the film uniformity. The data were then used to demonstrate the fabrication of uniform sol-gel chemistry derived porous polymer films inside 2mm inner diameter diamond shells.
An apparatus for characterization of a micro beam comprising a micro modified Faraday cup assembl... more An apparatus for characterization of a micro beam comprising a micro modified Faraday cup assembly including a first layer of material, a second layer of material operatively connected to the first layer of material, a third layer of material operatively connected to the second layer of material, and a fourth layer of material operatively connected to the third layer of
Damage to VUV, EUV, and X-ray Optics, 2007
Multilayers are artificially layered structures that can be used to create optics and optical ele... more Multilayers are artificially layered structures that can be used to create optics and optical elements for a broad range of x-ray wavelengths, or can be optimized for other applications. The development of next generation x-ray sources (high brightness synchrotrons and x-ray free electron lasers) requires advances in x-ray optics. Newly developed multilayer-based mirrors and optical elements enabled efficient band-pass filtering, focusing and time resolved measurements in recent FLASH (Free Electron LASer in Hamburg) experiments. These experiments are providing invaluable feedback on the response of the multilayer structures to high intensity, short pulsed x-ray sources. This information is crucial to design optics for future x-ray free electron lasers and to benchmark computer codes that simulate damage processes.
2009 IEEE International Conference on Plasma Science - Abstracts, 2009
Summary form only given. A scaled two-dimensional particle-in-cell model of a planar DC sputterin... more Summary form only given. A scaled two-dimensional particle-in-cell model of a planar DC sputtering magnetron is developed using the XOOPIC code1. The PIC model includes collisions through a Monte Carlo model, and includes the ability to calculate spatial, energy, and angular distribution functions for ions impacting arbitrary surfaces. Due to the large computational expense as well as a physical instability
19th Annual Symposium on Photomask Technology, 1999
We present recent experimental results from an actinic (operates at the EUV wavelength) defect in... more We present recent experimental results from an actinic (operates at the EUV wavelength) defect inspection system for extreme ultraviolet lithography mask blanks. A method to cross-register and cross-correlate between the actinic inspection system and a commercial visible-light scattering defect inspection system is demonstrated. Thus, random, real defects detected using the visible-light scattering inspection tool can be found and studied by our actinic inspection tool. Several defects with sub-100 nm size (as classified by the visible scattering tool) are found with the actinic inspection tool with a good signal to noise ratio. This result demonstrates the capability of the actinic inspection tool for independent defect counting experiments at a sub-100 nm defect sensitivity level.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2001
We present recent experimental results of actinic extreme ultraviolet lithography mask blank defe... more We present recent experimental results of actinic extreme ultraviolet lithography mask blank defect inspection. The detection sensitivity of the current actinic inspection system is predicted to be able to reach approximately 30 nm in cross correlation experiments done with commercial visible-light, SEM and AFM inspection tools. Random, native defects identified using the visible-light tool were scanned by the actinic tool and the scattering characteristics were compared. Scanning electron microscopy and atomic force microscopy (AFM) characterization of selected defects were also performed for physical measurement. We found a defect whose size was as small as 60 nm and AFM analysis showed that this defect was a 3 nm high substrate defect that was smoothed-out by the multilayer coating.
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Papers by Christopher Walton